1. Field of the Invention
The present invention relates to a battery pack and a charge control method used for a battery pack, and more particularly, to a battery pack and a battery capacity calculating method for calculating an appropriate battery capacity without using a correction table.
2. Description of the Related Art
In recent years, in portable electronic apparatuses such as laptop personal computers, cell phones, and PDAs (Personal Digital Assistants), battery packs using lithium-ion secondary batteries have been widely used as power sources thereof. The lithium-ion secondary batteries have advantages in lightweight, a large capacity, easiness of detecting a remaining capacity, and a long cycle life.
In a secondary battery of the battery pack, a full charge voltage and a discharge termination voltage are determined. A battery capacity at the discharge termination voltage is set to 0 mAh and a battery capacity at the full charge voltage is set to a so-called full charge capacity. In a case where the lithium-ion secondary battery is used, a battery voltage of 4.2 V is set for the full charge voltage and a battery voltage of 3.0 V is set for the discharge termination voltage for a single-cell lithium-ion secondary battery, for example. Then, actually flowing charging currents or discharge currents are integrated at a time of charge or discharge and thus the battery capacity can be calculated.
Further, as disclosed in U.S. Pat. No. 6,789,026 (hereinafter, referred to as Patent Document 1), a method of measuring a charge capacity using an OCV (Open Circuit Voltage) value of the secondary battery is also employed.
In such a method, there is a case where even when the integration result of the charging currents does not show a full charge capacity in a battery capacity calculation during the charge, full charge detection conditions like a condition in which the charging current takes a value equal to or lower than a charge termination current value are established. In this case, the battery capacity is forcibly corrected to a predetermined full charge capacity at a time at which the full charge detection conditions are established.
Further, there is also a case where the calculation result of the battery capacity exceeds the full charge capacity before the full charge detection conditions are established. In such a case, for example, after a remaining battery capacity ratio (so-called charge ratio) obtained based on the calculation result of the battery capacity becomes 99%, a user is being notified that the remaining battery capacity ratio is 99% by the time the full charge detection conditions are established even if the calculation result of the battery capacity exceeds the full charge capacity. When the full charge detection conditions are then established, the user is notified that the remaining battery capacity ratio is 100%.
It should be noted that since the charge capacity changes depending on a battery temperature, the integration result and the like are corrected using a temperature correction table.